Powersteering pump pulley wont stay aligned on 1992 Chevrolet 1500 Pickup

Start engine few minutes will start to back off then belt comes off also replaced belt idler pulley tensioner

Asked by for the 1992 Chevrolet 1500 Pickup
Remove belt, check all pulley's, if any are loose, either tighten them or replace. Check all bolts and bracket to P S pump. Inspect closely. Goodluck